Laser system for enhancing remineralization and strength of hard tissue

ABSTRACT

A laser-based system and method for treatment of hard tissue enhances remineralization and fluoride uptake to improve resistance to demineralization. The system can include a laser source, an optic, and a controller for controlling the laser source and/or the optic to deliver radiation to a treatment region with desirable characteristics (e.g., to remove carbonate without damaging the tissue surface). In some cases, the system includes a handpiece having an optical element (e.g., a lens) mounted within a replaceable cartridge and adapted to modulate a laser beam to render the beam non-ablative, prior to the laser beam&#39;s delivery to the treatment region. In some embodiments, treatment with the laser can be combined with a fluoride treatment for enhanced therapeutic effect.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. ProvisionalPatent Application No. 62/956,862 entitled “Laser System for EnhancingRemineralization and Strength of Hard Tissue,” filed on Jan. 3, 2020,the contents of which are incorporated by reference herein in theirentirety.

TECHNICAL FIELD

The present invention generally relates to the treatment of hard tissueusing a light-emitting device (e.g., a laser source) and, moreparticularly, to enhancing remineralization and strength of hard tissueby directing radiation emitted by a laser source to the hard tissue.

BACKGROUND

Dental caries is a disease where tooth mineral is dissolved by acid and,if it progresses, cavities are formed. Specific bacteria in the mouthform organic acids when they feed on fermentable carbohydrates, such assugar. These organic acids readily dissolve the carbonatedhydroxyapatite mineral of tooth enamel causing mineral loss(demineralization) that initially shows up as a non-cavitated “whitespot” that eventually becomes a cavity if the process continues.

The mineral that comprises about 95% by weight of tooth enamel is oftendescribed as being hydroxyapatite, which is a form of calcium phosphate.However, in actuality, tooth enamel contains numerous impurities andinclusions as a result of being formed in a biological fluid system inthe human body. The mineral is better described as a carbonatedhydroxyapatite in which about 1 in every 10 phosphate groups arereplaced by carbonate, making the mineral many-fold more soluble in acidthan pure hydroxyapatite, which has no carbonate inclusions.

Research has been performed on the use of lasers for the treatment ofcaries, e.g., by ablating decayed tissue so that it can be replaced witha filling material. Lasers such as Er:YAG and Nd:YAG lasers areprimarily absorbed by water within the tooth rather than hydroxyapatiteand may cause undesired damage to the tissue surface during a heatingprocess. This is partly because a significant amount of the water isremoved before hydroxyapatite reaches the high temperatures required forthe acid-resistant effect and also from a blasting effect, as the waterunder the surface turns to steam. More recent research has revealed thatcertain CO₂ laser wavelengths are better absorbed in hydroxyapatite andcan be effective in ablating dental tissue.

However, significantly less is known about the use of lasers to preventcaries formation and acid dissolution in the first place. Preliminaryacademic research has suggested that the enamel surface can be modifiedby heating it with short laser pulses and that such heating may lead toimproved caries resistance. However, significantly more research isneeded to determine the desired operating parameters for such lasertreatments and to adapt the academic research to a functional systemappropriate for commercial use with patients. Additionally, little isknow about the effects of such laser treatments in combination withconventional caries resistance treatments, such as fluorideapplications.

SUMMARY

Embodiments of the invention described herein relate to a lasertreatment system that can be used to enhance both strength andreminzeralization of hard dental tissue. In some implementations, theinvention includes the combined use of a laser treatment system andconventional treatment techniques such as fluoride applications, forenhanced effect. The inventors discovered that laser irradiation ofdental enamel that results in the removal of carbonate fromhydroxyapatite also improves the absorption of fluoride, resulting in afurther modified enamel surface that approaches the composition of theless soluble form of calcium phosphate known as fluorapatite, which iseven more resistant to acid attack than hydroxyapatite.

In various embodiments, the invention includes a laser source thatoperates in the wavelength range of 9-11 μm, such as a CO₂ laser. CO₂lasers have several advantages over other types hard tissue lasers(e.g., Er:YAG lasers), e.g., the absorption coefficient inhydroxyapatite is about 2 factors higher. The invention can feature ahandpiece for directing the 9-11 μm laser beam to a hard tissue surfacein the oral cavity with desirable efficiency, minimal techniquesensitivity, and a fast treatment time.

The system can be adapted to scan the laser beam using a variety ofscanning techniques, e.g., using galvo-mirrors. The laser beam can bescanned across the treatment region using particular pattern(s) to allowfor efficient energy delivery, producing enough localized photothermaleffect to contract collagen without damaging (burning or charring) thetissue. Some such patterns are described in more detail in U.S. PatentPublication No. 2017/0319277, which is incorporated herein by referencein its entirety and attached as Appendix A.

The system may also include a laser source controller than can adjustone or more treatment parameters (e.g., laser pulse duration) accordingto the type of treatment selected and/or the type of tissue beingtreated. Various treatment parameters are described in more detail belowand also in U.S. Patent Publication No. 2018/0325622, which isincorporated herein by reference in its entirety and attached asAppendix B.

In general, in one aspect, embodiments of the invention feature a systemfor treating a hard dental tissue. The system can include a laser sourcefor generating a laser beam, an optic in optical communication with thelaser source adapted to direct the laser beam to a treatment surface ofthe hard dental tissue, and a controller adapted to control the lasersource and the optic to deliver the laser beam to the treatment surfaceto treat an area of the hard dental tissue at a rate in a range from 10cm²/min to 20 cm²/min with a fluence in a range from 0.4 J/cm² up to 1.2J/cm² to: (i) remove at least some carbonate from the treatment surfaceto generate an acid resistant surface without damaging the hard dentaltissue, and (ii) reduce a ΔZ value of the hard dental tissue by at least10% relative to untreated hard dental tissue.

In various embodiments, the laser source can include a CO₂ laser source.The laser beam can include a wavelength in a range from 9 μm to 11 μm.In some instances, the laser beam can have a spot size at the treatmentsurface in a range from 0.2 mm to 5 mm. The optic can include agalvanometer and/or a turning mirror. In some instances, the controlleris further adapted to control the laser source to deliver the laser beamto the treatment surface in a series of pulses. In some cases, eachpulse in the series of pulses include a pulse energy in a range from 0.1mJ to 50 mJ. In some cases, each pulse in the series of pulses includesa pulse duration in a range from 1 μsec to 100 μsec. In some cases, eachpulse in the series of pulses includes a repetition rate in a range from0.05 Hz to 10 Hz. The series of pulses can include a duty cycle in arange from 0.1 to 10.

In some embodiments, the controller is adapted to deliver the series ofpulses to the treatment surface in a pattern. The pattern can include adiameter in a range from 1 mm to 5 mm. The pattern can include a numberof locations in a range from 1 to 1,000 (e.g., 217 locations). Thespacing between each location in the pattern can be in a range from 0.1mm to 5 mm. In some instances, the controller is also adapted to controlthe laser source to deliver the laser beam to the treatment surface to,when combined with a fluoride treatment, reduce a ΔZ value of the dentaltissue by at least 20% relative to hard dental tissue subject to thefluoride treatment. In some cases, the system can also include afluoride delivery system adapted to deliver the fluoride treatment tothe treatment surface. In some instances, the controller is furtheradapted to control the laser source to deliver the laser beam to thetreatment surface to reduce a ΔS value of the dental tissue by at least68% relative to untreated dental tissue. In some cases, the controlleris further adapted to control the laser source to deliver the laser beamto the treatment surface to, when combined with a fluoride treatment,reduce a ΔS value of the dental tissue by at least 18% relative to harddental tissue subject to the fluoride treatment.

In general, in another aspect, embodiments of the invention relate to amethod for treating a hard dental tissue. The method can include thesteps of: generating a laser beam using a laser source, directing thelaser beam to a treatment surface of the hard dental tissue using anoptic in optical communication with the laser source, and controllingthe laser source and the optic using a controller to deliver the laserbeam to the treatment surface to treat an area of the hard dental tissueat a rate in a range from 10 cm²/min to 20 cm²/min with a fluence in arange from 0.4 J/cm² up to 1.2 J/cm² to: (i) remove at least somecarbonate from the treatment surface to generate an acid resistantsurface without damaging the hard dental tissue, and (ii) reduce a ΔZvalue of the hard dental tissue by at least 10% relative to untreatedhard dental tissue.

In various embodiments, the laser source includes a CO₂ laser source.The laser beam can include a wavelength in a range from 9 μm to 11 μm.In some instances, the laser beam can have a spot size at the treatmentsurface in a range from 0.2 mm to 5 mm. The optic can include agalvanometer and/or a turning mirror. In some instances, the controlleris further adapted to control the laser source to deliver the laser beamto the treatment surface in a series of pulses. In some cases, eachpulse in the series of pulses include a pulse energy in a range from 0.1mJ to 50 mJ. In some cases, each pulse in the series of pulses includesa pulse duration in a range from 1 μsec to 100 μsec. In some cases, eachpulse in the series of pulses includes a repetition rate in a range from0.05 Hz to 10 Hz. The series of pulses can include a duty cycle in arange from 0.1 to 10.

In some embodiments, the controller is adapted to deliver the series ofpulses to the treatment surface in a pattern. The pattern can include adiameter in a range from 1 mm to 5 mm. The pattern can include a numberof locations in a range from 1 to 1,000 (e.g., 217 locations). Thespacing between each location in the pattern can be in a range from 0.1mm to 5 mm. In some instances, the controlling step further includesusing the controller to deliver the laser beam to the treatment surfaceto, when combined with a fluoride treatment, reduce a ΔZ value of thedental tissue by at least 20% relative to hard dental tissue subject tothe fluoride treatment. In some cases, the method can further includethe step of delivering the fluoride treatment to the treatment surface.In some instances, the controller is further adapted to control thelaser source to deliver the laser beam to the treatment surface toreduce a ΔS value of the dental tissue by at least 68% relative tountreated dental tissue. In some cases, the controlling step furtherinclude using the controller to control the laser source to deliver thelaser beam to the treatment surface to, when combined with a fluoridetreatment, reduce a ΔS value of the dental tissue by at least 18%relative to hard dental tissue subject to the fluoride treatment.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. In the following description,various embodiments of the present invention are described withreference to the following drawings, in which:

FIG. 1 is a schematic perspective view of a laser treatment system,according to various embodiments;

FIG. 2 is a schematic cross-sectional side view of a handpiece includingan optical cartridge, according to various embodiments;

FIG. 3 is an example plot of a beam size diameter vs. distance from thehandpiece exit orifice, according to various embodiments;

FIG. 4 is a depiction of an example treatment pattern, according tovarious embodiments;

FIGS. 5A-D depict lased and unlased tissue surfaces under varioustreatment conditions, according to various embodiments;

FIG. 6 depicts an experimental setup used to demonstrate performance ofthe laser treatment system, according to various embodiments;

FIG. 7 depicts another experimental setup used to demonstrateperformance of the laser treatment system, according to variousembodiments;

FIG. 8A is an example chart showing knoop hardness number measurementsof various tissue surfaces subject to different pH cycle tests,according to various embodiments;

FIG. 8B is an example plot depicting changes in hardness of varioustissue surfaces subject to different pH cycle tests, according tovarious embodiments;

FIG. 9 is an example chart showing ΔZ measurements of various tissuesurfaces subject to treatments at different fluence levels, according tovarious embodiments;

FIGS. 10A-C are an example charts showing ΔS measurements, surface lossmeasurements, and surface microhardness measurements, respectively, ofvarious tissue surfaces subject to treatments at different fluencelevels, according to various embodiments;

FIGS. 11A-B are graphs showing example ΔZ vs. ΔS measurements, accordingto various embodiments;

FIGS. 12A-C are a table and graphs showing example ΔS and ΔZmeasurements for various tissue surfaces subject to treatment atdifferent fluence levels, according to various embodiments; and

FIG. 13 is a chart providing example laser and treatment parametervalues, according to various embodiments.

DETAILED DESCRIPTION

In various embodiments, the present invention is directed to an improvedlaser treatment system 100. The system 100 can reduce caries formationand acid dissolution of treated hard dental tissue when compared withconventional devices. The system 100 can include a hand piece 1 thatdelivers laser pulses that heat the hard tissue to remove carbonateimpurities from the hydroxyapatite (and thereby enhanceremineralization/decrease demineralization) without damaging the tissue.As used herein, the phrase “damaging the tissue” refers to one ofburning, charring, or melting of the tissue. The removal of carbonatealone is not considered to be “damaging the tissue,” under thedefinition used herein. Removal of carbonate without damaging the tissueis further described in U.S. Patent Publication No. 2018/0325622, whichis incorporated herein by reference in its entirety and attached asAppendix B.

In various embodiments, the system 100 can also feature (i) a laser beamhaving a long working range (defined below), (ii) a coolant deliverysystem for delivering coolant (air, water, mist, etc.) to the oraltreatment region and optionally (iii) a fluoride delivery system forapplying fluoride to the treatment region. This application will oftendescribe treatment of a hard dental tissue; however, in general, theinventions described herein can be adapted to be used with any suitablehard tissue (e.g., jaw, skull, and other bone regions).

In some embodiments, the laser treatment system 100 includes a CO₂ lasersource 102 operating at a wavelength in a range of 9-11 μm (e.g., 9.3μm) and a handpiece 1 configured to enable uniform treatment of allteeth with minimal change in technique sensitivity. The system 100 canaccomplish treatment efficiently, with a fast treatment time and withoutneed for anesthesia.

As shown in FIG. 2, the handpiece 1 may be structured and designed toreceive an optical cartridge 2. The optical cartridge 2 can include atleast one optical lens to modulate a laser beam passing therethrough(e.g., to generate a collimated laser beam). For example, as shown inFIG. 2, the optical cartridge can include an upstream optical lens 3 anda downstream optical lens 4. The optical cartridge 2 can be retained inthe handpiece 1 using any known technique, e.g., with threading 6. Theability to replace or remove the optical cartridge 2 allows switchingthe laser between treatment modes, such as from an ablative mode to anon-ablative treatment mode and vice versa. In addition, the handpiece 1can include channels or tubing 5 to deliver non-laser substances to thetreatment region, e.g., cooling fluids (e.g., air, water, and mistcombinations thereof) and/or a fluoride based fluid to enhance acidresistance and improve fluoride uptake. The handpiece can include anexit orifice 8 out of which the laser beam is directed, in someembodiments via a turning mirror 7. In some embodiments, the laser beamcan be scanned through the hand piece and across a treatment regionusing galvanometers disposed upstream of the optical cartridge 2.

In some embodiments, the optical cartridge 2 can provide a laser beamhaving a relatively long working range. FIG. 3 is a plot of beamdiameter (1/e²) vs. distance from the exit orifice 8 of the handpiece 1,for a 1.0 mm beam generated with the optical cartridge 2 and for anative beam generated without the optical cartridge 2. The example datademonstrates the capability of the optical cartridge to produce acollimated and larger beam size (1 mm) than the original beam size (0.4mm) and uniform over long working range (e.g., 5-20 mm). Because fluenceis a measure of energy per unit area, generating a collimated beam andmaintaining a uniform beam area (spot size) along the length of thelaser beam (as opposed to a non-collimated beam that converges anddiverges about a focal point) can generate a laser beam having a lowerfluence which, in some instances, may result in the laser beam beingnon-ablative. The larger spot size can also enable for more surface areaof the treatment region (e.g., a tooth) to be covered more quickly,thereby reducing treatment time.

In various embodiments, the laser is pulsed and scanned according tocertain patterns to achieved desired levels of carbonate removal.Moreover, the laser source may be spatially scanned to provide differentpulse energies at different locations as shown in FIG. 4. In variousembodiments, laser and treatment parameters (e.g., as shown in FIG. 13)may be selected to optimize efficiency and to treat the tissue withoutdamage. Example treatment patterns are described in more detail in U.S.Patent Publication No. 2017/0319277 and U.S. Patent Publication No.2018/0325622, both of which are incorporated by reference herein intheir entireties and attached as Appendices A and B.

In various embodiments, the laser treatment system 100 can operate in amanner that improves the reduction of caries formation and enhancesremineralization. In particular, experiments have been conducted usingthe laser treatment system 100 to demonstrate this improved performance.

In a first example experiment, a 9.3 μm Solea CO₂ laser (ConvergentDental, Inc., Needham, Mass.) was used with a beam diameter of 1 mm(measured by 1/e² method) that was collimated at the output of thehandpiece over a range of 5 centimeters. The beam was scanned at arepetition rate of 750 Hz using a pair of controllable mirrors(galvanometers) in a pattern with a uniform spacing between centers ofadjacent hits of 0.2 mm and a maximum frequency between adjacent hits of25 Hz. This distribution of hits allowed the energy to be dissipatedwithout accumulation of heat in the pulp. To assist in cooling, aregulated, system-delivered air flow from the handpiece was used on thesamples while irradiating with the laser. Laser fluence was varied onlyby changing the optical pulse duration between 17-27 μs. At 17 μs, theaverage power is 3.5 W and fluence per pulse is 0.6 J/cm². At 27 μs, theaverage power is 5.7 W and fluence per pulse is 1.0 J/cm². The distancefrom the handpiece to the tooth samples was maintained at a set positionof 10 mm to further ensure uniform delivery of energy and air to thetreatment surface.

To investigate the formation and properties of an acid resistant layer,five sound human enamel samples mounted in acrylic resin and polished to1 μm diamond grit finish (Therametrics, Inc., Indianapolis, Ind.) wereused. The laser-treated blocks had only been exposed to thymol solutionduring shipment and were less than 3 months old from extraction. TheSolea CO₂ 9.3 μm laser was used with a pulse fluence range of 0.6-1J/cm2. The blocks were serially polished up to 6 μm grit from the sideto expose a cross-section of both the laser-irradiated andnon-irradiated areas. The original surface that had beenlaser-irradiated was masked with an acid-resistant tape. Thecross-section surface was exposed to 1N HCl for 1 min to erode theunderlying ordinary enamel and expose the acid resistant layer, thenrinsed thoroughly with water. The blocks were imaged under a 3D digitalreflection microscope (Hirox RH-2000) with cross-polarization to capturethe subsurface characteristics. The microscope was used to obtain 3Dstacks of images over a range of depth of 50 μm.

FIG. 5A is a cross-sectioned image of enamel exposed to hydrochloricacid. In this example, an acid-resistant layer in the range of about 15μm is created by laser-irradiation at a fluence of 0.8 J/cm² and isexhibited as an undissolved protrusion above the underlying enamel thathad experienced a rapid dissolution and is out of focus in themicroscope image. FIG. 5B shows a cross section of the enamel for thenon-irradiated section that dissolved uniformly with no acid-resistantlayer observed. This served as a verification that the laser parametersused in the above experiment successfully formed an acid resistant layeron the enamel surface to inhibit demineralization. FIGS. 5C and 5D are3-dimensional image stacks of the enamel samples that reveal the acidresistant layer as an unetched area near the surface for the laserirradiated sample, and a flat, evenly etched area for the non-irradiatedsample.

In a second example experiment, to investigate reduction of caries andcaries-like legions and the correlation with inhibition of surfacemineral loss, seventy-four human molars with no signs of caries orfluorosis and that were less than 3 months old since extraction wereobtained and stored only in thymol solution. The molars were mounted in1″ acrylic cylinders with the full crown exposed (all sides and occlusalsurface) (Therametrics, Inc., Indianapolis, Ind.). The samples weresonicated for 5 minutes in distilled water. The samples were then airdried and split into six groups. Groups 1-3 underwent pH cycling withoutadditional fluoride and groups 4-6 with additional fluoride. Groups 1and 4 were laser-irradiated at a fluence of 0.6 J/cm², groups 2 and 5 at0.8 J/cm², and groups 3 and 6 at 1.0 J/cm² on either side of theflattest area (least curvature) of the side of the crown as shown inFIG. 6. Example collected data is shown in Table 1 and Table 2 below(some loss of samples occurred due to polishing damage or otherimmeasurability of the sample). A non-irradiated control area wasmaintained in between the laser-irradiated areas. An acid-resistant,quick curing nail polish was used to mask the boundaries betweenlaser-irradiated and non-irradiated regions along the entire height ofthe molar from the mounted base to the occlusal surface. FIG. 6 depictsa human molar in an acrylic resin mount. Laser-irradiated areas L1 andL2 are depicted, along with the non-irradiated control, C. The stripesare the masked regions over the full height of the exposed tooth.

TABLE 1 pH Cycling Depth Data Laser Lased Lased Non-lased Non-lasedLased Additional Fluence ΔZ ΔZ ΔZ ΔZ Reduction p-value Group Fluoride(J/cm²) (std) n (std) n % ΔZ (95%) 1 No 0.6 1025 (253)^(a) 13 1610(247)^(e) 13 36.3 p = 0.001 2 No 0.8 763 (322)^(ab) 15 1809 (498)^(e) 1557.8 p < 0.001 3 No 1.0 374 (149)^(bcd) 5 1826 (325)^(e) 7 79.5 p =0.002 4 Yes 0.6 349 (54.1)^(cd) 12 591 (103)^(b) 12 40.9 p < 0.001 5 Yes0.8 216 (145)^(d) 13 665 (176)^(b) 13 67.5 p < 0.001 6 Yes 1.0 113(62.9)^(d) 7 572 (172)^(bc) 8 80.2 p = 0.01  Groups that share alower-case letter are not significantly different.

TABLE 2 pH Cycling Surface Data Laser Lased Lased Non-lased Non-lasedLased Additional Fluence ΔS ΔS ΔS ΔS Reduction p-value Group Fluoride(J/cm²) (std) n (std) n % ΔS (95%) 1 No 0.6 71.8 (17.1)^(ab) 10 124(26.7)^(e) 10 42.1 p = 0.002 2 No 0.8 55.4 (15.4)^(bc) 15 107 (29.4)^(e)15 48.2 p < 0.001 3 No 1.0 40.6 (3.6)^(cd) 5 113 (27.6)^(ae) 5 64.1 p =0.004 4 Yes 0.6 56.9 (15.1)^(bc) 11 92.1 (17.8)^(ae) 11 38.2 p = 0.006 5Yes 0.8 39.1 (5.4)^(d) 13 100.1 (35.7)^(ae) 13 60.9 p < 0.001 6 Yes 1.032.5 (8.4)^(d) 7 88.2 (23.4)^(abe) 7 63.2 p < 0.001 Groups that share alower-case letter are not significantly different.

Demineralization solution was made in the form of a 75 mM acetate bufferwith 2 mM calcium and phosphate, pH balanced to 4.4 using NaOH or HClwhere needed. Remineralization solution was made from 0.1 M Tris, 0.8 mMcalcium and 2.4 mM phosphate, pH balanced to 7.1. A 9-pH-cycle regimenwith the aforementioned solutions was followed similar to the onedescribed in Rechmann P, Rechmann B M T, Groves W H, et al., “Cariesinhibition with a CO₂ 9.3 μm laser: An in vitro study,” Lasers Surg Med.2016; 554(February):1-9, doi:10.1002/lsm.22497, with steps of 6 hours indemineralization and 18 hours in remineralization. Approximately halfthe samples were exposed to a fluoride-toothpaste slurry for 1 min aftereach step in the cycle, using a 1:3 ratio of Crest cavity protection1,100 ppm F toothpaste (Proctor and Gamble, Inc.) to distilled water.After 5 cycles, the solutions were replaced with fresh solutions fromthe same batch. After cycling, samples were stored in distilled waterfor no more than two weeks until the measurements were performed.

The samples were polished up to 6 at a time using an automated polisher(Metkon Forcipol 1V) with a 600 grit polishing pad until a flatcross-section in the laser-irradiated areas was reached. The sampleswere individually hand polished with a diamond suspension to removepolish marks for microhardness testing. The samples were seriallyindented (Matsuzawa Seiki DMH-2) using 25 g loads for 10 s each every 25μm under the surface, starting at 15 μm from the outer surface until adepth of 200 μm was reached. The volume percent mineral content wascalculated at each indentation position using the formula vol %=4.3√{square root over (KHN)}+11.3, and ΔZ, a measure of depth mineral loss,was calculated as the area under the curve (with 85% as the normalizedlevel for sound enamel), as described in Stookey G K, Featherstone J DB, Rapozo-Hilo M, et al., “The Featherstone laboratory pH cycling model:A prospective, multi-site validation exercise,” Am J Dent. 2011;24(5):322-328.

After ΔZ was determined, each sample was turned on its side so that thelaser-irradiated areas were facing up. Samples were then polished onthis same side until half of the sample had been removed. Occasionalloss of sample occurred due to unexpected damage to the surface ormishandling. Using the same indenter, samples were indented 10 times onthe laser-irradiated and non-irradiated control surfaces on each region.The symmetry and quality of each indent was checked under the microscopeand the lengths of the indents were measured. Surface loss was thenmeasured at the edge of the nail polish using the built-in 3D stage onthe microscope. It was determined as the change in height from the edgeof the masked surface to the top of the adjacent unmasked enamelsurface. Measurements were taken along the entire length of the boundaryregion at least every 50 μm, obtaining at least 10 measurements for eachboundary region. The surface loss and hardness measurements werecombined as ΔS=h2/(h1+h2)*vol % as depicted in FIG. 7, where vol % iscalculated from the indents as described above. FIG. 7 depicts a diagramof creating an indent on enamel (left) and a cross-sectional view of theindent site (right). For the calculation of ΔS, h1=surface loss,h2=microhardness indent height, and vol % is calculated from the size ofthe indent on the surface. ΔS is a representation of the amount ofmineral loss on the surface relating to a slow surface mineral loss;whereas, ΔZ is a measure of mineral loss in depth relating to acaries-like formation under the surface. Data were analyzed on alog-scale using Welch's ANOVA and post-hoc Games-Howell tests betweengroups. FIG. 8A is an example chart showing knoop hardness numbermeasurements of various tissue surfaces subject to different pH cycletests, according to various embodiments. FIG. 8B is an example plotdepicting changes in hardness of various tissue surfaces subject todifferent pH cycle tests, according to various embodiments.

ΔZ values, shown in Table 1 and FIG. 9, provide a measure of caries-likelesion formation and serve as a metric for comparing treatments withdifferent laser settings. For the range of fluences used, there were noobserved superficial structural changes. However, there were occasionalsigns of minor fracture-like structural changes under the surface forthe areas irradiated with 1.0 J/cm², possibly related to subsurfacethermal fracturing.

Welch's ANOVA applied to the data showed that there were significantdifferences between the groups (F_(11,40)=81.0, p<0.001). The averagereduction in ΔZ from use of additional fluoride (groups 4-6) withoutlaser-irradiation was ˜65% (p<0.001). Reductions in ΔZ from laserirradiation alone were observed (see groups 1-3 in Table 1), whichindicates that an effective remineralization can and does occur, with orwithout the presence of additional fluoride. Post-hoc Games-Howell testsshowed that the combination treatment of laser-irradiation andadditional fluoride provided the most significant benefit in reducing ΔZfor each of the laser fluences used (p<0.01 for all). AlthoughpH-cycling with fluoride toothpaste alone revealed a benefit in cariesinhibition, application of fluoride toothpaste in an area that had beenirradiated as described herein resulted in the most significant andunexpectedly high reduction in caries formation, with as high as a ˜92%(p=0.001) reduction in ΔZ compared to the untreated control areas.

Table 2 and FIGS. 10A-10C show a combination of the surface metrics, inthe form of ΔS. As with ΔZ, Welch's ANOVA applied to ΔS values showedthat there were significant differences between groups (F_(11,36)=39.5,p<0.001). ANOVA showed no differences within the non-irradiated groupswithout additional fluoride (F_(2,12)=1.16, p>0.05) or with additionalfluoride (F_(2,16)=0.22, p>0.05). The general trends for ΔS were similarto those observed for ΔZ in relation to laser fluence. ΔS values showedno significance from fluoride use alone relative to untreated controlsthrough post-hoc Games-Howell tests (p>0.05). However, comparing alldata without additional fluoride to that with additional fluoride usingStudent's t-test, a significant reduction of ΔS by ˜18% (p<0.001) wasfound. ΔS revealed that laser-irradiation alone at 9.3 μm inhibitssurface mineral loss by as much as ˜64% (p=0.004). Furthermore, acombination of 1 J/cm² laser-irradiation coupled with fluorideapplication from toothpaste showed an unexpectedly high reduction insurface mineral loss of ˜72% (p<0.001) compared to the untreatedcontrol.

FIG. 11A is a plot of ΔZ values as a function of ΔS values for themeasurements collected in the above-described experiment. ΔZ and ΔSvalues followed a log-normal distribution, and a linear trend betweenthem was observed with a Spearman rho of 0.63 (p<0.001). FIG. 11B showslinear regression fits (on a log scale) when the data points wereaveraged according to treatment group. Since the control andtoothpaste-cycled sets were different in methodology, they are treatedas distinct sets. The linear fits for these two sets have very similarslopes, ˜1.3, both with an R²≥0.95. This discovery provides two veryimportant pieces of information. One is that the overall effect offluoride on caries and acid resistance can be quantified by the verticalshift in the curve, revealing that fluoride provides a 50-60% inhibitionin caries formation/acid penetration. The other is that the benefit ofthe laser can be quantified for each pulse fluence. Averaged both withand without additional fluoride, ΔZ and ΔS were remarkably improved by˜39%, 59%, and 72% after laser-irradiation of 0.6, 0.8 and 1.0 J/cm²,respectively, compared to areas without laser-irradiation.

FIG. 12A provides example data, including ΔZ and ΔS measurements, fortissues lased at various fluences and with and without the applicationof fluoride. FIG. 12B is a graph of measured ΔZ values for variousfluences for treatments combined with fluoride and without fluoride, aswell as an indication of an example effective treatment zone. FIG. 12Cis a graph of measured ΔS values for various fluences for treatmentscombined with fluoride and without fluoride, as well as an indication ofan example effective treatment zone.

In various embodiments, laser irradiation at 9.3 μm creates anacid-resistant form of hydroxyapatite that occurs at temperatures inwhich a large amount of the carbonate groups in thecarbonated-hydroxyapatite mineral of the dental enamel are removed. Thiscan allow a crystallization of fluoride-containing hydroxyapatite inthese weak areas to occur, thereby reducing the penetration of acidunder the resistant layer. Other organic components, which largely existas a glue-like network holding adjacent rods together, may also beremoved near the surface during irradiation. This surface change hasbeen described previously as a “glazing” of the surface.

In various embodiments, the benefit of laser-irradiation under the laserconditions tested, even without the use of fluoride, is significant. Thesoftening of the surface and formation of an underlying lesion can beslowed significantly. This may be an indication that a crystallizationof the “weakened” sites occurs from dissolved minerals (primarilycalcium and phosphate), despite an initial acid exposure. Due to thisremineralization effect, the benefit of laser-induced acid resistancecan, outweigh the risks associated with structural changes to thesurface. In some embodiments, the introduction of fluoride in thecycling process can enhance the acid resistant properties of the layer,which may be due at least in part to the inherent resistance offluorapatite to dissolution. The laser treated area may encourage anuptake of fluoride by the surface, together with calcium and phosphate,resulting in the observed beneficial effect of the pair of treatments incombination. As described below, in some embodiments that application offluoride can be performed with delivery of the coolant with the lasertreatment system 100. However, the invention also contemplates deliveryof fluoride from other sources, e.g., separate from delivery through thelaser treatment system 100, either as part of a dental office visit orelsewhere (e.g., brushing teeth or using mouthwash at home).

The inventions described herein demonstrate a direct correlation betweenthe surface mineral loss (ΔS) and the size of a carious lesion (ΔZ). Insome embodiments, one explanation for this is that a completeremineralization back to the original density may not be possible, asthe crystallization is random and may introduce insufficiently packedcrystals. Through laser irradiation of the surface, the softening of theenamel from acid exposure may be significantly reduced, which wasevident in both measures of surface (erosion) or depth (caries) mineralloss. The resistance to acid may be further enhanced by use of ahigh-concentration fluoride application, such as prescription mouthwashor varnish, which would also help to quickly remineralize any weak siteswith fluorapatite, possibly even before a patient leaves the treatmentclinic, as the laser-irradiated area is capable of increasing the rateof fluoride uptake. In this work, erosion and caries resistance may beenhanced by around 50-60% using fluoride-containing toothpaste and canbe increased by a further 40-80% using a laser treatment with a 9.3 μmCO₂ laser.

As used herein, the term “working range” means the distance along thelength of the laser beam at which the laser beam has a fluence capableof treating the tissue (e.g., removing carbonate). Conventional deviceshave a relatively short working range, typically focused tightly arounda focal point of the laser beam based on a desire to not waste anyenergy along the length of the laser. The laser treatment system of thepresent invention can, in some embodiments, tolerate a longer workingrange, so as to enable an operator to move their hand (and,correspondingly, the laser beam), while still treating the treatmentarea effectively. In other words, in certain embodiments, the amount ofenergy delivered to the target tissue does not change over a relativelylong distance along the axis between the exit orifice 8 and the hardtissue (e.g., more than 0.5 cm, more than 1 cm, more than 1.5 cm, morethan 2 cm, more than 3 cm, more than 4 cm, etc.) to accommodate for handmovements, variability in the user's holding of the handpiece standoffand other human factors. The concept of a working range is described inmore detail with reference to the phrase “depth of treatment” (which canbe interchanged with “working range”) in U.S. Patent Publication No.2016/0143703, which is incorporated by reference herein in its entiretyand attached as Appendix C.

In some embodiments, the hand piece 1 can also be adapted to transmitfluids to the treatment region, e.g., cooling fluids and/orfluoride-based fluids. The fluids can be transported using any knowntechnique, e.g., through fluid tubing 5 that run along the handpiece 1and bypass the optical cartridge 2. The cooling fluids can be useful tominimize and avoid excessive heating of the tissue. As discussed above,the fluoride based fluids may result in improved and more effectivetreatment. In some cases, both cooling and fluoride based fluids can bedelivered through the same tubings 5. In other cases, the hand piece 1can include separate tubing for each of the cooling fluid andfluoride-based fluid. Other desirable fluids may also be transportedthrough the hand piece 1.

In certain embodiments, the laser beam is accompanied with a markingbeam (e.g., green in color) that serves as guidance of the location ofthe laser beam on the target tissue. In some instances, the irradiationof the laser may occur in a pattern. A visual or sonar feedback canoptionally be integrated within the system 100 to indicate to the userthe need to move to a new target area. A visual feedback indicating anew target area can include a stationary guidance beam (e.g., a greenpoint projected on the tissue). For example, while the tissue is beingexposed to the laser, a pattern can be displayed on the tissue. Whenenough energy has been delivered, the laser can stop scanning and apoint object can being projected on the target tissue. Alternatively, asonar feedback can be provided to indicate a pattern and/or amount ofenergy delivery.

FIG. 13 is a chart including example laser and operation parameters forthe laser treatment system 100. The parameters may be designed to have adesired outcome efficiency to remove carbonate without damaging thetreatment surface material. In some embodiments, the laser beam may bespatially scanned to provide different pulse energy at differentlocations, as will be appreciated by those skilled in the art.

Each numerical value presented herein is contemplated to represent aminimum value or a maximum value in a range for a correspondingparameter. Accordingly, when added to the claims, the numerical valueprovides express support for claiming the range, which may lie above orbelow the numerical value, in accordance with the teachings herein.Every value between the minimum value and the maximum value within eachnumerical range presented herein (including the low, nominal, and highvalues shown in the chart shown in FIG. 13), is contemplated andexpressly supported herein, subject to the number of significant digitsexpressed in each particular range.

Having described herein illustrative embodiments of the presentinvention, persons of ordinary skill in the art will appreciate variousother features and advantages of the invention apart from thosespecifically described above. It should therefore be understood that theforegoing is only illustrative of the principles of the invention, andthat various modifications and additions, as well as all combinationsand permutations of the various elements and components recited herein,can be made by those skilled in the art without departing from thespirit and scope of the invention. Accordingly, the appended claimsshall not be limited by the particular features that have been shown anddescribed but shall be construed also to cover any obvious modificationsand equivalents thereof.

What is claimed is:
 1. A system for treating a hard dental tissue, thesystem comprising: a laser source for generating a laser beam; an opticin optical communication with the laser source adapted to direct thelaser beam to a treatment surface of the hard dental tissue; and acontroller adapted to control the laser source and the optic to deliverthe laser beam to the treatment surface to treat an area of the harddental tissue at a rate in a range from 10 cm²/min to 20 cm²/min with afluence in a range from 0.4 J/cm² up to 1.2 J/cm² to: remove at leastsome carbonate from the treatment surface to generate an acid resistantsurface without damaging the hard dental tissue; and reduce a ΔZ valueof the hard dental tissue by at least 10% relative to untreated harddental tissue.
 2. The system of claim 1, wherein the laser sourcecomprises a CO₂ laser source.
 3. The system of claim 2, wherein thelaser beam comprises a wavelength in a range from 9 μm to 11 μm.
 4. Thesystem of claim 1, wherein the laser beam comprises a spot size at thetreatment surface in a range from 0.2 mm to 5 mm.
 5. The system of claim1, wherein the optic comprises at least one of a galvanometer and aturning mirror.
 6. The system of claim 1, wherein the controller isfurther adapted to control the laser source to deliver the laser beam tothe treatment surface in a series of pulses.
 7. The system of claim 6,wherein each pulse in the series of pulses comprises a pulse energy in arange from 0.1 mJ to 50 mJ.
 8. The system of claim 6, wherein each pulsein the series of pulses comprises a pulse duration in a range from 1μsec to 100 μsec.
 9. The system of claim 6, wherein the series of pulsescomprises a repetition rate in a range from 0.05 Hz to 10 Hz.
 10. Thesystem of claim 6, wherein the series of pulses comprises a duty cyclein arrange from 0.1 to
 10. 11. The system of claim 6, wherein thecontroller is adapted to deliver the series of pulses to the treatmentsurface in a pattern.
 12. The system of claim 11, wherein the patterncomprises a diameter in a range from 1 mm to 5 mm.
 13. The system ofclaim 11, wherein the pattern comprises a number of locations in a rangefrom 1 to 1,000.
 14. The system of claim 13, wherein the patterncomprises 217 locations.
 15. The system of claim 13, wherein a spacingbetween each location in the pattern is in a range from 0.1 mm to 0.5mm.
 16. The system of claim 1, wherein the controller is further adaptedto control the laser source to deliver the laser beam to the treatmentsurface to, when combined with a fluoride treatment, reduce a ΔZ valueof the dental tissue by at least 20% relative to hard dental tissuesubject to the fluoride treatment.
 17. The system of claim 16, furthercomprising a fluoride delivery system adapted to deliver the fluoridetreatment to the treatment surface.
 18. The system of claim 1, whereinthe controller is further adapted to control the laser source to deliverthe laser beam to the treatment surface to reduce a ΔS value of thedental tissue by at least 68% relative to untreated dental tissue. 19.The system of claim 18, wherein the controller is further adapted tocontrol the laser source to deliver the laser beam to the treatmentsurface to, when combined with a fluoride treatment, reduce a ΔS valueof the dental tissue by at least 18% relative to hard dental tissuesubject to the fluoride treatment.
 20. A method for treating a harddental tissue, the method comprising the steps of: generating a laserbeam using a laser source; directing the laser beam to a treatmentsurface of the hard dental tissue using an optic in opticalcommunication with the laser source; and controlling the laser sourceand the optic using a controller to deliver the laser beam to thetreatment surface to treat an area of the hard dental tissue at a ratein a range from 10 cm²/min to 20 cm²/min with a fluence in a range from0.4 J/cm² up to 1.2 J/cm² to: remove at least some carbonate from thetreatment surface to generate an acid resistant surface without damagingthe hard dental tissue; and reduce a ΔZ value of the hard dental tissueby at least 10% relative to untreated hard dental tissue. 21.-38.(canceled)